Neoplastic cells show an increased glucose metabolism and glycolysis which is associated with high lactate concentrations. There is also data for several tumor entities that high levels of lactate in the tumor are associated with tumor progression, metastasis and poor clinical outcome. Kreutz et al. demonstrated that diclofenac inhibits tumor cell proliferation in vitro and tumor growth in vivo via COX-independent effects on glucose metabolism. Diclofenac is taken up by tumor cells and inhibits tumor cell proliferation through inhibition of the oncogene MYC and subsequently glycolysis and block of lactate transport. MYC regulates genes involved in glycolysis and is upregulated in neoplastic cells, which is in line with the metabolic switch to glycolysis, the so called "Warburg effect", that cancer cells show. Although these results were found in vitro using human melanoma cells and in vivo in a mouse model, a similar mechanism of action is assumed to be relevant for the treatment of actinic keratoses with topical diclofenac. However tumor metabolism in diclofenac-treated actinic keratoses has never been investigated. To investigate the mechanism of action of diclofenac in the treatment of actinic keratoses, a clinical study analyzing particularly lactate levels, glycolysis and inflammatory infiltrate is needed.